This invention relates to roller-hearth brazing furnaces through which parts to be brazed are conveyed and brazed, and more particularly, to the method of controlling the timing of feeding parts into the furnace.
Roller-hearth brazing furnaces are used to braze components of a part assembly together, such as the blades or fins in a torque converter for an automatic transmission. The joints of the components to be brazed together are coated with a brazing compound, such as a copper based brazing compound. The part assembly is then passed through the brazing furnace which melts the copper in the copper brazing compound. The melted copper reflows into the joints of the components being brazed together and, as the copper cools and solidifies, brazes the components together.
A roller-hearth brazing furnace has an entry door, an outlet door, and a conveyer extending through a plurality of heating zones and a cool-down zone between the entry and outlet doors. One conventional brazing furnace has four heating zones and a cool-down zone. Trays of part assemblies, the components of which are to be brazed together, are successively fed into the furnace through the entry door and are continuously conveyed on the conveyor through the heating zones. As the trays of parts pass through the heating zones, the temperature of the parts is progressively raised in a known controlled manner to the melting point of copper, which flows into the joints of the elements of the parts to be brazed together. After leaving the last heating zone, the trays are conveyed through the cool-down zone, where the part assemblies are cooled in a known controlled manner, and exit the furnace through the exit door.
The trays of part assemblies are staged at the entry door of the furnace and successively fed into the furnace. One typical method of controlling the feeding of the trays into the furnace is to feed a tray of part assemblies into the furnace at fixed timed intervals. The timed interval, which typically can be adjusted, is set so that the furnace has the opportunity to recover after the tray enters the furnace.
A problem with using a fixed time interval to control the feeding of trays into the furnace is that it results in sub-optimum throughput due to different part assemblies being run through the furnace, or trays being less than fully loaded. The amount of time that it takes the furnace to recover after a tray is fed into the furnace through the entry door depends on the mass of the part assemblies on the tray. Consequently, when successive trays have different part assemblies, the total mass of the part assemblies on the successive trays differ. In order to ensure that the furnace has sufficient time to recover after a tray containing the most massive part assembly enters the furnace, the fixed time interval must be set at the time interval appropriate for the most massive part assembly. However, when a tray containing less massive part assemblies enters the furnace, the furnace recovers quicker than the fixed time interval and there is then a non-productive period where the furnace could accept another tray but one is not fed into the furnace until fixed time interval expires. A similar problem occurs when trays are less than fully loaded.
It is an object of this invention to improve the productivity of roller-hearth brazing furnaces by monitoring the recovery time of the furnace and adjusting the time interval at which trays are fed into the furnace to minimize the non-productive period.